Cleaning device with deeply reaching plasma and assisting electrodes

Abstract

A cleaning device with deeply reaching plasma and assisting electrodes has supporting racks, a chamber, a plasma sources, metallic grids. Flat boards to be cleaned such as circuit boards are located in the supporting racks. The supporting racks are disposed in the chamber. The metallic grids are disposed on two sides of the chamber. The plasma source is disposed next to the metallic grids. Electric voltage is applied to the metallic grids such that plasma from the plasma source can be pushed deeply into the supporting racks to evenly and sufficiently clean the circuit boards.

What is claimed is:  
     
       1. A plasma cleaning system for deep cleaning workpieces comprising: 
       (a) a vacuum chamber, said vacuum chamber containing a gas introduced therein;  
       (b) at least one supporting rack disposed in said vacuum chamber, said supporting rack having first and second end portions;  
       (c) first and second plasma sources disposed to respectively oppose said first and second end portions of said supporting rack, said first and second plasma sources being operable to generate a plasma; and,  
       (d) at least one metallic grid defining member disposed between each of said supporting rack first and second end portions and said first and second plasma sources, each said metallic grid defining member being actuated responsive to a predetermined electric voltage signal applied thereto for increasing the charge density of the plasma within said supporting rack.  
     
     
       2. The plasma cleaning system as recited in  claim 1  wherein said metallic grid defining member includes a mesh structure having a mesh opening width within the approximate range of 1 to 20 millimeters. 
     
     
       3. The plasma cleaning system as recited in  claim 1  wherein said metallic grid defining member includes a metallic plate having a plurality of through holes formed therein. 
     
     
       4. The plasma cleaning system as recited in  claim 1  wherein said predetermined electric voltage signal is of a type selected from the group consisting of: a positive voltage direct current signal, a negative voltage direct current signal, a positive unipolar pulsed signal, and a negative unipolar pulsed signal. 
     
     
       5. The plasma cleaning system as recited in  claim 1  wherein said predetermined electric voltage signal is a bipolar pulsed signal. 
     
     
       6. The plasma cleaning system as recited in  claim 1  wherein said predetermined electric voltage signal is disposed in frequency within an intermediate frequency range. 
     
     
       7. The plasma cleaning system as recited in  claim 1  wherein said predetermined electric voltage signal is disposed in frequency within an approximate range of 40 KHz to 13.56 MHz. 
     
     
       8. The plasma cleaning system as recited in  claim 1  comprising a plurality of said supporting racks disposed substantially in parallel one relative to the other. 
     
     
       9. The plasma cleaning system as recited in  claim 8  wherein said supporting racks are each formed of a conductive material for conducting a predetermined auxiliary electric signal applied thereto, said supporting racks being electrically isolated within said vacuum chamber by at least one insulating cushion. 
     
     
       10. The plasma cleaning system as recited in  claim 9  wherein said predetermined auxiliary electric voltage signal is of a type selected from the group consisting of: a positive voltage direct current signal, and a negative voltage direct current signal. 
     
     
       11. The plasma cleaning system as recited in  claim 9  wherein said predetermined auxiliary electric voltage signal is a pulsed voltage signal pulsed at a frequency within an approximate range of 0.1 to 500 KHz. 
     
     
       12. The plasma cleaning system as recited in  claim 9  wherein said predetermined auxiliary electric voltage signal is an intermediate frequency alternating current signal having a frequency within an approximate range of 0.1 to 500 KHz. 
     
     
       13. The plasma cleaning system as recited in  claim 8  further comprising a plurality of holding members receiving said supporting racks. 
     
     
       14. The plasma cleaning system as recited in  claim 13  wherein said supporting racks are each formed of a conductive material for conducting a predetermined bias signal applied thereto, said holding member being formed of an insulating material. 
     
     
       15. The plasma cleaning system as recited in  claim 13  wherein said supporting racks are each formed of a conductive material for conducting a predetermined bias signal applied thereto, said holding members being formed of a conductive material, said supporting racks being electrically isolated from said holding members by a plurality of insulating cushions disposed therebetween. 
     
     
       16. The plasma cleaning system as recited in  claim 13  wherein said supporting racks are each formed of a conductive material, said holding members being formed of a conductive material for conducting a predetermined bias signal applied thereto, said supporting racks being electrically isolated from said holding members by a plurality of insulating cushions disposed therebetween. 
     
     
       17. The plasma cleaning system as recited in  claim 1  wherein said first and second plasma sources each include an inductively-coupling portion. 
     
     
       18. The plasma cleaning system as recited in  claim 17  wherein said first and second plasma sources each include an antenna receiving a high frequency power signal. 
     
     
       19. The plasma cleaning system as recited in  claim 1  wherein said first and second plasma sources each include a hollow cathode discharge portion. 
     
     
       20. The plasma cleaning system as recited in  claim 1  wherein said first and second plasma sources each include a hollow cathode discharge portion, each said hollow cathode discharge portion defining one said grid defining member. 
     
     
       21. The plasma cleaning system as recited in  claim 19  or  20  wherein said hollow cathode discharge portions define hollow negative electrodes respectively disposed opposing said first and second end portions of said supporting rack, said hollow negative electrodes each having a plurality of through holes formed therein, said hollow negative electrodes generating a flow of negative plasma responsive to the application of a predetermined negative voltage signal thereto. 
     
     
       22. The plasma cleaning system as recited in  claim 1  wherein said first and second plasma sources each include at least one of a helicon coupling and capacitive coupling portions. 
     
     
       23. The plasma cleaning system as recited in  claim 8  further comprising first and second magnetic field members respectively disposed adjacent said first and second plasma sources for generating a magnetic field directed therebetween. 
     
     
       24. The plasma cleaning system as recited in  claim 23  wherein said first and second magnetic field members each include a permanent magnet.